The present invention relates generally to the use of Ceramic Matrix Composite liners in a gas turbine engine combustor and, in particular, to the sealing of such CMC liners with a support member for the combustor at an aft end in a manner that accommodates differences in radial and axial growth therebetween.
It will be appreciated that the use of non-traditional high temperature materials, such as Ceramic Matrix Composites (CMC), are being studied and utilized as structural components in gas turbine engines. There is particular interest, for example, in making combustor components which are exposed to extreme temperatures from such material in order to improve the operational capability and durability of the engine. As explained in U.S. Pat. No. 6,397,603 to Edmondson et al., substitution of materials having higher temperature capabilities than metals has been difficult in light of the widely disparate coefficients of thermal expansion when different materials are used in adjacent components of the combustor. This can result in a shortening of the life cycle of the components due to thermally induced stresses, particularly when there are rapid temperature fluctuations which can also result in thermal shock.
Accordingly, various schemes have been employed to address problems that are associated with mating parts having differing thermal expansion properties. As seen in U.S. Pat. No. 5,291,732 to Halila, U.S. Pat. No. 5,291,733 to Halila, and U.S. Pat. No. 5,285,632 to Halila, an arrangement is disclosed which permits a metal heat shield to be mounted to a liner made of CMC so that radial expansion therebetween is accommodated. This involves positioning a plurality of circumferentially spaced mount pins through openings in the heat shield and liner so that the liner is able to move relative to the heat shield.
U.S. Pat. No. 6,397,603 to Edmondson et al. also discloses a combustor having a liner made of Ceramic Matrix Composite materials, where the liner is mated with an intermediate liner dome support member in order to accommodate differential thermal expansion without undue stress on the liner. The Edmondson et al. patent further includes the ability to regulate part of the cooling air flow through the interface joint.
Another concern with the implementation of CMC liners is providing a seal with other metal hardware. Besides taking into account the differences in thermal growth, the CMC material is very abrasive since a part made from such material includes multiple layers of fabric and essentially has a woven appearance. Accordingly, this makes it difficult to produce a long lasting seal due to the wear thereon. It will also be understood that the support pieces of prior combustors have generally been welded to the metal liners, but this approach is not available since CMC cannot be welded to metal.
It will be appreciated that the sealing of air between an aft end of the combustor liner and a turbine nozzle located downstream thereof is also desired. While sealing in this area has occurred previously with metal liners, it has heretofore been accomplished in conjunction with a hard connection, such as through welding, between the liner and an adjacent support member. According to the CMC construction of the liners in the present combustor, however, such sealing must occur in an environment where there is only a seal between the liner and adjacent support member.
It will be noted that a mounting assembly has been disclosed in a patent application entitled “Mounting Assembly For The Aft End Of A Ceramic Matrix Composite Liner In A Gas Turbine Engine Combustor,” having Ser. No. 10/326,209, and owned by the assignee of the present invention. Such mounting assembly takes into account the differences in thermal growth created by the respective coefficients of thermal expansion of the liners made of ceramic matrix composite and the support members made of metal. The mounting assembly therein, however, involves a sliding connection between the liner and support member which may cause axial loads to be incurred. Further, the liner is typically required to incorporate additional thickness at its aft end to accommodate the aforementioned pin configuration.
Accordingly, it would be desirable for a sealing assembly to be developed for use with a combustor having a CMC liner, where such sealing assembly is able to accommodate differences in radial and/or axial growth between such liner and an adjacent support member of the combustor while maintaining a seal to prevent air from entering the combustor flow path. It is also desirable for the sealing assembly to avoid hard connections between the support member.